Modern vehicles are often equipped with vehicle controllers which assist the driver in certain driving situations such as during braking, accelerating, or in critical driving situations. Among such controls are, for example, anti-lock braking systems (ABS), traction controls (TCS/ASR) or vehicle-dynamics controllers (e.g., ESP). These systems usually determine the vehicle linear velocity from the rotational speed of the individual wheels. The speed estimated in this manner is normally used to calculate setpoint values for specific vehicle variables such as a setpoint yaw rate, for example.
During a control intervention, e.g., in an ABS situation, the wheel speeds can deviate heavily from the vehicle velocity. In an ABS situation, because of the brake slip, the wheel speeds are usually considerably lower than the corresponding actual vehicle velocity. In such situations the vehicle linear velocity can be determined only inadequately. In vehicles having two-wheel drive it is possible that one of the wheels is underbraked so that it basically rotates freely, and to use the rotational speed of the underbraked wheel to calculate the vehicle linear velocity. However, this is not an option in the case of vehicles with all-wheel drive and equipped with a center lock since all wheels of the vehicle are linked to one another in terms of power via the center lock, and the front wheels thus have a retroactive effect on the wheels of the rear axle and vice versa. It is therefore impossible to exempt an individual wheel independently of the others. During an ABS braking operation, the linear velocity of a vehicle having all-wheel drive with a center lock can thus be determined only inadequately.